The present invention relates generally to flexural pivots and more particularly relates to a multi-piece flexural pivot which requires fewer parts and is more cost effective to manufacture than prior art flexural pivots.
Prior art flexural pivots are typically fabricated by brazing four quadrants, inner and outer flexural members, and a sleeve into a flexural pivot assembly. The described arrangement has a plurality of brazed joints which are prone to fracture when the pivot is subjected to vibration and shock loading. Failures in which individual quadrants of the four quadrants separate from the flexural members and outer sleeve, or in which the pivot core separates from the outer sleeve, by fracturing at the brazed joints are common.
Another problem encountered with brazed flex pivots using an outer sleeve is a condition called xe2x80x9cbridgingxe2x80x9d. Bridging occurs when the braze material used to join the pivot and core to the outer sleeve flows into an undercut area of the pivot and hence prevents flexing.
Further, the manufacturing processes for these prior art flex pivots are lengthy and include a variety of expensive, labor intensive operations. The resulting flex pivot has a high cost and a long manufacturing lead time. This prevents the flex pivot from being used in many applications where it would otherwise be advantageous.
Thus, it is an object of this invention to provide a flex pivot which only needs to be heat treated once, thereby reducing the chances for bridging, embrittlement, and flexure warping.
It is a further object of this invention to provide a flex pivot in which fewer assembly operations will be required.
It is a further object of this invention to provide a reduction in cost and manufacturing lead time for flex pivots.
It is a further object of this invention to utilize a one piece core which replaces the use of four quadrants in prior art flex pivots.
It is a further object of this invention to utilize a uniform thickness of the inner wall of the core to eliminate the thin quadrant pieces found in prior art flex pivots.
In a preferred embodiment of the present invention, component parts for constructing a flexural pivot include a tubular core having an unslotted end and a slotted end, a first and second pair of diametrically opposed unconnected and spaced apart flexure slots extending from the slotted end and partially into the tubular core ending at a point prior to reaching the unslotted end, each flexure slot having a length and, first and second interlocking flexures, wherein the interlocking flexures are positioned within the tubular core such that two sides of the first interlocking flexure are positioned within the first pair of diametrically opposed flexure slots and two sides of the second interlocking flexure are positioned within the second pair of diametrically opposed flexure slots. Preferably, each flexure slot in the tubular core extends a substantially equal distance from the slotted end. Each flexure slot may be positioned approximately 90 degrees from an adjacent flexure slot, or at other angular orientations if desired.
The tubular core may include a pair of diametrically opposed travel slots extending from the slotted end into the tubular core and positioned approximately 45 degrees from adjacent flexure slots, or at other angular orientations if desired, and each travel slot may extend further into the tubular core than each of the flexure slots, while the travel slots may be substantially equal in length to each other.
The first interlocking flexure may comprise a flat inner spring and the second interlocking flexure may comprise a flat outer spring, the inner spring fitted within the outer spring, the outermost sides of the interlocking flexures being substantially straight and equal in length to the length of the flexure slots so that abutment of the flexures at the end of a flexure slot results in flush positioning of the flexures with the slotted end of the core.
The component parts of the flexural pivot may further include a first sleeve and a second sleeve, the first sleeve having a first inner radius and a second inner radius, the first inner radius being greater than the second inner radius, the second sleeve having a third inner radius and a fourth inner radius, the third inner radius being greater than the fourth inner radius where the first sleeve and second sleeve are sized to slide over the tubular core. Preferably, a combined length of the first sleeve and second sleeve is slightly less than the length of a flexure slot so that a space can be left between the two sleeves.
In fabricating a multi-piece flexural pivot using the above-described component parts, a method is described herein which includes the steps of forming a slotted tubular core with a slotted end and an unslotted end, sliding at least two flexures within slots of a slotted section of the slotted tubular core so as to be flush with the slotted end, placing first and second sleeves over the core so that the first and second sleeves do not touch each other and the second sleeve is flush with the slotted end, and, cutting off an unslotted section of the core including the unslotted end. The step of forming the slotted tubular core preferably comprises cutting two pairs of diametrically opposed flexure slots for receiving the at least two flexures and for dividing the slotted end into quadrants and the step of sliding at least two flexures within slots comprises inserting the flexures within the flexure slots until they abut an end of the slots. Prior to the step of sliding the two flexures within the flexure slots, the method may include the step of interlocking an inner flexure in an outer flexure and forming a pair of interlocking flexures having sides substantially equal in length to the flexure slots.
The method may further comprise cutting a pair of diametrically opposed travel slots into the slotted end of the tubular core.
Further, the method may include the step, prior to sliding the two flexures within slots, of applying a bonding material to the core and holding the tubular core at its unslotted end for assembly and of placing the tubular core, flexures, and sleeves within a furnace and heating until the bonding material flows and bonds the flexures, core, and sleeves together.
Alternatively, the method may comprise the step of welding together the flexures to the core prior to placing the first and second sleeves on the core and then welding the sleeves in position on the core, prior to cutting the unslotted section off the core.